硫脲有機催化

在有機催化領域， （硫）脲有機催化指利用脲或硫脲來加快有機反應速率或控制立體化學。與經典的催化方法不同，這種催化方法的利用的是底物和（硫）脲之間形成的氫鍵作用（可以認為發生「部分質子化」）。（硫）脲有機催化的應用包括立體選擇性應用與非立體選擇性應用^[1]

歷史

Kelly、Etter、Jorgensen、Hine、Curran、Göbel和De Mendoza（參見下文引用的參考文獻）在非金屬小分子氫鍵催化領域作出了開創性貢獻。Peter R. Schreiner及其同事確定並引入了缺電子的硫脲衍生物作為氫鍵有機催化劑。Schreiner的選擇的硫脲為N,N'-二[3,5-二(三氟甲基)苯基]硫脲，這種催化劑結合了雙氫鍵介導的有機催化劑的所有結構特徵：

• 缺電子
• 具有剛性結構
• 苯環的3,4 和/或 5 位上具有非配位吸電子取代基
• 3,5-二(三氟甲基)苯基是優選的取代基

催化劑-底物相互作用

硫脲衍生物和羰基底物之間形成了兩個氫鍵。（硫）脲中共面的兩個氨基取代基是氫鍵的給體。^{[2] [3] [4] [5]} 方醯胺利用雙氫鍵進行催化的性能通常優於硫脲。 ^[6]

Schreiner使用的N,N'-雙[3,5-雙（三氟甲基）苯基硫脲形成的酮絡合物，具有明顯的雙氫鍵螯合的特徵 ^{[4] [7]}

硫脲有機催化劑的優點

（硫） 脲是符合綠色化學理念要求的催化劑，在應用中具有以下優勢：

• 由於氫鍵的結合焓相對較低，因此（硫）脲催化劑的活性通常不會被產物抑制，但是可以特異性識別底物
• 催化劑用量低（可以低至0.001 mol%）^[3]
• 高TOF （周轉頻率）值（高達 5,700 h^-1 ） ^[3]
• 可以由（手性）伯胺與異硫氰酸酯反應合成，較為簡單、廉價
• 性質較穩定，易於處理，不需要惰性氣體氛圍保護
• 可以固定在固相聚合物上，便於催化劑回收與重複使用^[3]
• 可以在中性、溫和條件下進行催化（pK_a(硫脲) = 21.0, DMSO）^[8]，可兼容對酸敏感的底物
• 不含金屬，與傳統含金屬的路易斯酸催化劑相比毒性更小
• 耐水，甚至在水溶液體系中仍然具有催化能力^[9]

底物

可接受氫鍵的底物包括羰基化合物、亞胺、硝基烯烴。 Diels-Alder反應也可以受（硫）脲催化。

催化劑

已開發出多種單官能和雙官能的手性雙氫鍵（硫）脲有機催化劑，以催各種可以用於合成的有機反應。

• 
  1998: Jacobsen將手性席夫鹼硫脲衍生物（結合在聚合物上）用於不對稱Strecker反應^{[10] [11]}
• 
  2003: Takemoto將雙官能手性硫脲衍生物用於不對稱Michael反應和Aza-Henry反應的催化 ^[12]
• 
  2004: Nagasawa利用手性雙硫脲有機催化劑催化不對稱貝利斯-希爾曼反應 ^[13]
• 
  2005: Nagasawa利用雙功能硫脲官能化的胍不對稱催化亨利反應^[14]
• 
  2005: Ricci利用帶有額外羥基的手性硫脲衍生物，催化吲哚與硝基烯烴發生有對映選擇性的傅克烷基化^[15]
• 
  2005: Wei Wang利用雙官能聯萘硫脲衍生物，不對稱催化Morita-Baylis-Hillman反應^[16]
• 
  2005: Soos、Connon和Dobson利用雙官能硫脲官能化的金雞納生物鹼催化硝基烷不對稱地與查爾酮 ^[17] 以及丙二酸酯加成^[18]
• 
  2006: Yong Tang利用手性雙官能吡咯烷硫脲催化環己酮對硝基烯烴的對映選擇性麥可加成^[19]
• 
  2006: Takemoto使用PEG結合的手性硫脲，不對稱催化反式-β-硝基苯乙烯的（串聯）麥可反應的氮雜-亨利反應。^[20]
• 
  2007: Kotke/Schreine使用與聚苯乙烯結合的硫脲衍生物，催化醇的四氫吡喃化^[3]
• 
  2007: Wanka/Schreiner利用手性肽金剛烷硫脲催化Morita-Baylis-Hillman反應^[21]
• 
  2007: Takemoto利用螯合的雙官能羥基硫脲催化喹啉的對映選擇性Petasis型反應^[22]
• 
  2007: Ma Jun-An基於糖的手性雙官能伯胺和叔胺硫脲催化劑^{[23] [24]}

拓展閱讀

• Christian M. Kleiner, Peter R. Schreiner. Hydrophobic amplification of noncovalent organocatalysis. Chem. Commun. 2006: 4315–4017.
• Z. Zhang and P. R. Schreiner. Thiourea-Catalyzed Transfer Hydrogenation of Aldimines. Synlett. 2007, 2007 (9): 1455–1457. doi:10.1055/s-2007-980349.
• Wanka, Lukas; Chiara Cabrele; Maksims Vanejews; Peter R. Schreiner. γ-Aminoadamantanecarboxylic Acids Through Direct C–H Bond Amidations. European Journal of Organic Chemistry. 2007, 2007 (9): 1474–1490. ISSN 1434-193X. doi:10.1002/ejoc.200600975. 

參考文獻

1. Kotke, Mike; Schreiner, Peter R. (Thio)urea Organocatalysts. Petri M. Pihko (編). Hydrogen Bonding in Organic Synthesis. October 2009: 141 to 251 [2022-01-15]. ISBN 978-3-527-31895-7. （原始內容存檔於2014-01-15）.
2. Alexander Wittkopp, Peter R. Schreiner, "Diels-Alder Reactions in Water and in Hydrogen-Bonding Environments", book chapter in "The Chemistry of Dienes and Polyenes" Zvi Rappoport (Ed.), Volume 2, John Wiley & Sons Inc.; Chichester, 2000, 1029-1088. ISBN 0-471-72054-2.
   
   Alexander Wittkopp, "Organocatalysis of Diels-Alder Reactions by Neutral Hydrogen Bond Donors in Organic and Aqueous Solvents", dissertation written in German, Universität Göttingen, 2001. English abstract/download:
   
   Peter R. Schreiner, review: "Metal-free organocatalysis through explicit hydrogen bonding interactions", Chem. Soc. Rev. 2003, 32, 289-296. abstract/download:
   
   M. Kotke and P. R. Schreiner. Acid-free, organocatalytic acetalization. Tetrahedron. 2006, 62 (2–3): 434–439. doi:10.1016/j.tet.2005.09.079.M. P. Petri. Activation of Carbonyl Compounds by Double Hydrogen Bonding: An Emerging Tool in Asymmetric Catalysis. Angewandte Chemie International Edition. 2004, 43 (16): 2062–2064. PMID 15083451. doi:10.1002/anie.200301732.
   
   Yoshiji Takemoto, review: "Recognition and activation by ureas and thioureas: stereoselective reactions using ureas and thioureas as hydrogen-bonding donors", Org. Biomol. Chem. 2005, 3, 4299-4306. abstract/download: Mark S. Taylor, Eric N. Jacobsen. Asymmetric Catalysis by Chiral Hydrogen-Bond Donors. Angewandte Chemie International Edition. 2006, 45 (10): 1520–1543. PMID 16491487. doi:10.1002/anie.200503132.J. C. Stephen. Organocatalysis Mediated by (Thio)urea Derivatives. Chemistry: A European Journal. 2006, 12 (21): 5418–5427. PMID 16514689. doi:10.1002/chem.200501076.
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